Lecture 10 Flashcards
(21 cards)
Substrate utilizzation during exercise
- 30 minute bouts
during exercise, a significant quantity of metabolic substrate comes from the blood
plasma FFA - decreases as VO2max invtensity increases
plasma glucose - increases as VO2max intensity increases
blood glucose homeostasis
maintenance of blood glucose levels during exercise is critically important
1. glucose is a major substrate for metabolism
2. glucose is the only fuel acceptable to the brain and other CNS tissues
normal resting blood glucose concentration:
- 4.0 - 5.5 mmol/L
- 90 - 100 mg/dL
exercise increase glucose uptake from blood
muscle contraction —> increase AMP/ATP ratio —> AMPK
to GLUT - 4 VESISCLE to the plasma membrane
from the blood vessel, glucose goes through GLUT - 4 in the plasma mmbrane —> then is converted to ATP (energy)
maintaining blood glucose during exercise
we do not store much glucose in our blood…
example: 70 kg person has a blood volume of 5 L
- blood glucose = 100mg/dL (or 1g/L)
- total stored blood glucose = 5 grams
- each g of glucose provides 5 kcal/L of oxygen (total = 25 kcal)
if glucose stored in blood were the only fuel, and its use was not immediately compensated for, blood [glucose] would fall rapidly!
blood glucose response to exercise
glucose increases until it is remained at an elevated level
how do we replenish blood glucose?
in the liver glycogenolysis and gluconeogenesis can replenish glucose into the blood stream
increase release of glucose into the blood from liver, gut, and kidneys
when blood glucose falls in the blood, the liver replenishes the blood glucose
hepatic glucose production
catabolic - glycogenolysis
- glycogen uses enzymes glycogen phosphorylase, glucose - 1 - phosphate, phosphoglucomutase, to create glucose-6-phosphate, then use glucose-6-phosphatase enzyme to create glucose, which increases blood glucose
anabolic - gluconeogensis
- lactic acid and/or pyruvic acid, uses gylcerol from lipids (DHAP), some amino acids (oxalic acid), alaine (amino acids) and then convert to glucose-6-phosphate then to glucose increasing blood glucose
lipid mobilization
adipose tissue (white adipose cells) which are full of trglyceriders, lipolysis breaks down triglycerides to free fatty acids
blood-plasma goes to glycerol, FFA - albumin - FFA
muscle - intramuscular triglyceride to adn from fatty acids —> then to beta oxidation cycle — then into the mitochondria to acetylene-CoA, then krebs cycle and electron transport —> then out of the mitochondria to form ATP (energy) with the help of oxygen
increase circulating levels of alternative substrates (e.g. free fatty acids)
how does the body “know” to increase glucose production in liver or to mobilize fat stores?
glucose regulation during exercise
maintenance of glucose homeostasis during exercise requires physiological regulation:
1. endocrine system (hormones) —> chemical communiction
2. nervous system —> electrical communication
- sympathetic nervous system specifically
the endocrine system
- controls all physiological processes that support exercise and maintain homeostasis
- it does this by releasing hormones - hormones signaling molecules, produced and released by glands that are transported by the circulatory system to target organs where they act to regulate physiology
- we will focus on the major endocrine glads and their hormones that are relevant to the control of exercise metabolism
about hormones
secretion
- secreted in pulsatile bursts (plasma concentration fluctuates by min to hours, day to weeks)
- triggered by negative feedback — correcting an “error signal” — like your thermostat!
receptors
- bind tospecific receptors (no receptor - no effect)
- e.g. insulin binds to insulin receptor; norepinephrine binds to alpha receptors
action
- exert effects after binding with receptor — do not directly affect cell activity
- initiate a predictable series of reactions
- through protein synthesis
- act indirectly
endocrine glands
important for metabolic regulation
1. pancreas
2. adrenal gland
3. anterior pituitary gland
4. thyroid gland
- hormones released by these glands regulate the mobilization (adipose regulation) of metabolic fuels from energy stores in various tissues and the uptake and utilization of those fuels by working muscle
pancreas — endocrine regulation of metabolism
insulin : lowers blood glucose
- counters hyperglycemia, opposes glucagon
- facilitates glucose transport into cells
- enhances synthesis of glycogen, protein, fat
- inhibits gluconeogenesis
glucagon : raises blood glucose
- counters hypoglycemia, opposes insulin
- promotes glycogenolysis, gluconeogenesis
blood glucose control: negative feedback
blood glucose increase to the pancreas (beta cells), then insulin is released, then insulin tells muscle and liver to take in glucose, then blood glucose lowers, so now replenished and stops releasing into pancreas
blood glucose decreases (alpha cells) and releases glucagon, increase in blood glucose from the liver, than raise glucose, then stops release
in type 1 diabetes = absolutes insulin deficiency
- 1. No insulin production
in ype 2 diabetes = impaired glucose control
- 1. inadequate insulin production
- insulin isn’t released from the pancreas
- 2. reduced effect of insulin
- blood glucose is released from the pancreas, insulin is delivered to the muscle and liver, however they don’t respond as well, anddon’t take up blood glucose, which then causes glucose to remain raised and hyperglycemia can occur
insulin-stimulated glucose uptake
insulin released right after increase of glucose
blood vessel —> insulin —> insulin sensitive receptor —> P13K —> glut-4 vesicle
blood vessel —> glucose —> plasma membrane —> glut-4 vesicle —> transferred to ATP and glucogen
glucose regulation by pancreatic hormones during exercise
- in a healthy individual, during moderate-to-heavy (sub-CI) exercise, blood glucose does not change much even after 3 hours!
- this is because:
- 1. insulin concentration falls
- less glucose uptake more plasma glucose
- 2. glucagon concentration rises
- more liver glycogenolysis and glucose release
fun fact: during exercie, insulin concentration dcrease; cellular insulin sensitivity increases; nd more glucose is taken up into cells, and less insulin is used
glucagon rises during prolonged exercise
glucose only raised maybe 10%
glucagon rises (almost doubles) andstays at an elevated level
adrenal medulla
- endocrine regulation of metabolism
- located above each kidney
- releases catecholamines (“fight or flight”):
- epinephrine (Epi) and norepinephrine (NE) exercise —> increase sympathetic nervous sstem —> increase Epi and NE release
- stimulate glycogenolysis in uscle and liver
- stimulate carbohydrate metabolism
- stimulate and maintains lipolysis (Epi)
- maintain fat metabolism (release of free fatty acids)
- suppress insulin secretion
increase delivery of glucose and FFA to active muscle
- heart rate, contractile force, blood pressure
- blood flow to skeletal muscle
Epi and NE rise during prolonged exercise
both norepinephrine and epinephrine increase
- as exercise continues their effects arise, increase fat metabolism, to stop using carbohydrate metabolism
summary of Metabolic Effects of Hormones
celular glucose uptake
- perservation of carbohydrates and uptake
- hormone used is insulin
glycogen synthesis
- hormone used is insulin
triglyceride synthesis (decrease blood glucose)
- decrease in blood glucose
- hormone used is insulin
liver glycogenolysis
- increase liver function
- hormones used are glucagon, epinephrine, and norepinephrine
liver gluconeogenesis
- effects of glucagon
- hormone used is glucagon
muscle glycogenolysis
- increase in arbohydrate metabolism
- hormones used are epinephrine, norepinephrine and cortisol
lipolysis
- stimulated by cortisol
- hormone growth
- mobilizing fat —> for metabolism
- hormones used are cortisol, epinephrine, and growth hormone
substrate utilization changes during exercise
- skeletal muscle preferred source of fuel is stored glycogen
- wthprolonged exercise, muscle glycogen stores are depleted and we rely increasingly more on delivery of fat in the form of free fatty acids
- also, glucose must remain available to other tissue (brain)
- hormones regulate the shift in substrate utilization and moilization of fat and carbohydrate stores
